Abstract

This thesis reports the results of first-principles computational studies of thirteen
crystalline structures in the H2O-NH3 system. This includes eight low- and highpressure
polymorphs of pure water ice, two polymorphs of solid ammonia, and three
low-pressure stoichiometric ammonia hydrates. These simulations have been used to
determine the athermal equation of state (EoS) of each phase.
Where empirical data was lacking, experiments have been undertaken. Hence, this
thesis also reports the results of time-of-flight neutron scattering studies of deuterated
ammonia dihydrate powders down to 4 K, and up to a maximum pressure of 8.6 GPa.
In addition, I have developed a flexible and accurate planetary model that can be
used to calculate the triaxial shape and gravitational field of any object, regardless of
size or composition, given an assumed mineralogical constitution and provided the EoS
of said minerals are known. The EoS parameters found in this work have therefore been
used to model the structure and thermal evolution of icy moons orbiting Saturn in
anticipation of the Cassini spacecraft arriving at Saturn in mid-2004. Models of Rhea,
Saturn’s second largest moon, suggest that its volatile component is likely to contain > 3
weight percent ammonia, but that one is unlikely to be able to constrain the bulk
chemistry of the ice mantle from Cassini flyby data.

Type:

Thesis
(Doctoral)

Title:

Computational and experimental studies of solids in the ammonia-water system.

Open access status:

An open access version is available from UCL Discovery

Language:

English

Additional information:

Table of contents within thesis to be used as a guide, pagination does not exactly match that within full text file